A new stress corrosion cracking (SCC) susceptibility index, ISCC, is proposed in constant strain rate SCC test both for transgranular (TG)SCC and for inter-granular (IG)SCC. ISCC is best defined by the equation Isec=Asec/Amech are the area of SCC fractured surface and that of mechanically fractured surface, respectively. It is found that there is a good correlation between ISCC in constant strain-rate test and the time to fracture in constant load test.